Every American Indian and Native Alaskan tribal government is different, and each tribe has a different requirement, known as a blood quantum, for establishing membership. At a federal level, the US Bureau of Indian Affairs and the Department of the Interior have no requirement of this nature.
An individual's genealogy helps establish a relationship to a given tribe. Being able to clearly show direct familial relationship to someone who either is or was on tribal roles is often enough. This often requires research on the part of the applicant, though individuals who are already well known to those within the tribe itself and the tribal government are likely to have a helping hand available. With this in mind, an individual tribe is not required to establish a blood quantum requirement, nor is it required to restrict membership to only those whose lineage can be traced back to recognized tribal members. In most cases, it is a person's knowledge of tribal culture, history and language which play a primary role in their acceptance, with their lineage and familial relations acting mostly as a formality. For specific information about an individual tribe's requirements for membership, it is necessary to contact its internal governing body directly.